1. Field of the Invention
The present invention relates to a device (hereafter referred to as a light emitting device) having an element (hereafter referred to as a tight emitting element) in which a thin film made from a light emitting material is sandwiched between a pair of electrodes (an anode and a cathode). In particular, the present invention relates to a light emitting device having a light emitting element which uses a thin film made from a light emitting material in which EL (electroluminescence) is obtained (the light emitting element is hereafter referred to as an EL element).
2. Description of the Related Art
The development of light emitting devices having EL elements (hereafter referred to as EL light emitting devices) has advanced in recent years. Passive matrix and active matrix type EL light emitting devices exist, and each type operates by the principle in which a thin film, made from a light emitting material in which EL is obtained in accordance with the flow of electric current, within the EL element is made to emit light.
Various applications can be expected to utilize this type of EL display device, but its use in portable devices, in particular, due to the thinness of the EL display device and its light weight have been in the spotlight. The formation of light emitting elements on flexible plastic films have therefore been tested.
TFTs having electrical properties nearly as good as those of TFTs formed on glass substrates cannot be formed at present without lowering the maximum process temperature because the heat resistance of plastic films is low. High performance light emitting devices using plastic films have therefore not been achieved.
Further, a structure of a general EL element is shown in FIG. 18. An anode 12, a light emitting layer 13, and a cathode 14 are laminated on an insulating body 11 in FIG. 18, forming an EL element 10. A metallic electrode having a small work coefficient is generally used in the cathode 14, which is a supply source for electrons, and an oxide conductive film having a large work coefficient and which is transparent with respect to visible light (typically an ITO film) is used in the anode 12, which is a supply source for holes. This is done because the cathode 14, made from the metallic electrode, is not transparent with respect to visible light, and therefore light generated by the light emitting layer (hereafter referred to as EL light) cannot be observed.
In this case, EL light 15 passes directly through the anode 12 and is observed, or passes through the anode 12 after being reflected by the cathode 14 and is then observed. Namely, an observer 16 can observe the EL light 15 which has passed through the anode 12 for pixels in which the light emitting layer 13 emits light.
However, outside light 17 (light from outside the light emitting device) made incident to pixels which do not generate light is reflected by the rear surface of the anode (the surface contacting the light emitting layer), and there is a problem in that the rear surface of the cathode acts as a mirror and the external environment is shown on the observation surface (surface pointed toward an observer). Further, in order to avoid this problem, there is a method in which a circular polarizing film is attached to the observation surface of the EL light emitting device so that the external environment is not shown on the observation surface, but the circular polarizing film is extremely expensive, and thus invites a further problem of an increase in production costs.